Hemoglobin Goblins

I was just trying to do my civic and moral duty by donating blood, but it seems my right hand knoweth not what my left hand doeth. The blood-taker-person poked my left-hand finger, tested the blood, and said my hemoglobin was too low. But I had an option: if I wanted someone else to test blood from my other hand, the numbers might be higher.
I've never heard of such a thing. But it was true. My right hand had enough hemoglobin that they took a blood donation from my right arm.
All I can say is, my body parts had better quit hoarding the blood and start sharing. All for one, and all that.